package fr.gdi.android.news.api;

import java.security.SecureRandom;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

public class SimpleCrypto
{
    public static String encrypt(String seed, String cleartext) throws Exception
        {
            byte[] rawKey = getRawKey(seed.getBytes());
            byte[] result = encrypt(rawKey, cleartext.getBytes());
            return toHex(result);
        }
        
        public static String decrypt(String seed, String encrypted) throws Exception
        {
            byte[] rawKey = getRawKey(seed.getBytes());
            byte[] enc = toByte(encrypted);
            byte[] result = decrypt(rawKey, enc);
            return new String(result);
        }
        
        private static byte[] getRawKey(byte[] seed) throws Exception
        {
            KeyGenerator kgen = KeyGenerator.getInstance("AES");
            SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
            sr.setSeed(seed);
            kgen.init(128, sr); // 192 and 256 bits may not be available
            SecretKey skey = kgen.generateKey();
            byte[] raw = skey.getEncoded();
            return raw;
        }
        
        private static byte[] encrypt(byte[] raw, byte[] clear) throws Exception
        {
            SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
            Cipher cipher = Cipher.getInstance("AES");
            cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
            byte[] encrypted = cipher.doFinal(clear);
            return encrypted;
        }
        
        private static byte[] decrypt(byte[] raw, byte[] encrypted) throws Exception
        {
            SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
            Cipher cipher = Cipher.getInstance("AES");
            cipher.init(Cipher.DECRYPT_MODE, skeySpec);
            byte[] decrypted = cipher.doFinal(encrypted);
            return decrypted;
        }
        
        public static String toHex(String txt)
        {
            return toHex(txt.getBytes());
        }
        
        public static String fromHex(String hex)
        {
            return new String(toByte(hex));
        }
        
        public static byte[] toByte(String hexString)
        {
            int len = hexString.length() / 2;
            byte[] result = new byte[len];
            for (int i = 0; i < len; i++)
                result[i] = Integer.valueOf(hexString.substring(2 * i, 2 * i + 2), 16).byteValue();
            return result;
        }
        
        public static String toHex(byte[] buf)
        {
            if (buf == null) return "";
            StringBuffer result = new StringBuffer(2 * buf.length);
            for (int i = 0; i < buf.length; i++)
            {
                appendHex(result, buf[i]);
            }
            return result.toString();
        }
        
        private final static String HEX = "0123456789ABCDEF";
        
        private static void appendHex(StringBuffer sb, byte b)
        {
            sb.append(HEX.charAt((b >> 4) & 0x0f)).append(HEX.charAt(b & 0x0f));
        }
        
}

